The present invention relates to rods used for mounting structures in cryostats. The cryostat is a containing vessel designed to thermally isolate its interior from exterior ambient temperature conditions. To achieve the desired degree of thermal isolation, multiple nested vessels are generally employed with each of the multiple vessels functioning at one of a sequence of temperatures. The interior temperature of the inner-most vessel of the dewar is at the coldest temperature.
The vessels and the magnet have to be supported. The support structure should have minimal heat conductivity. For example, the magnet has to be supported within the dewar and yet spaced apart from the walls of the dewar with sufficient rigidity to withstand the shifting loads caused by the high magnetization of the magnet; i.e., 2 Tesla, for example. These loads include loads caused by hysteresis currents. Typically, in a magnetic resonance system, the inner-most vessel is a helium containing vessel which surrounds the superconducting magnet.
Heat shields help to isolate the nested vessels from each other. In most cryostats used in magnetic resonance systems, an innermost helium vessel is surrounded by a vessel containing nitrogen. Support rods are used to support the magnet and keep it stationary in three-dimensions by balancing out the magnet's weight and the forces generated by the magnetic field. The support rods are generally comprised of oppositely disposed stainless steel head sections and a low thermally conductive extended rod-like section connecting the head sections. The prior art head sections each has a threaded horn-like section and a receiving cylindrical bore containing-section. The low thermally conductive section fits into a bore of the bore containing section. The head sections are then crimped to the low thermally conductive section.
One horn-like threaded section is threaded into an outer nut means that retains and secures the support rod to the outer vacuum container. The head section at the other end of the low thermally conductive section of the support rod is connected to the actual magnet. The relatively long head section in the above described presently available support rod causes the support rod to conduct a relatively large amount of heat from outside the cryostat to the superconducting magnet.
It is an object of the present invention to provide a magnetic resonance cryostat that use a new support rod system wherein the support rod is designed to minimize heat conducted to the superconducting magnet from the ambient environment external to the cryostat.
In accordance with one preferred aspect of the present invention, a support rod for supporting structures in a dewar of a cryostat used in a magnetic resonance system is provided, said support rod comprising:
a rod-like mid-section of low thermally conductive material, PA1 a first head section of material of higher thermal conductivity than the material of said rod-like mid-section disposed on one end of said rod-like mid-section, PA1 a second head section of material of higher thermal conductivity than the material of said rod-like mid-section disposed on the other end of said rod-like mid-section, PA1 means for connecting said first head section of the support rod to structure in the interior of the cryostat, PA1 means for connecting said second head section to the outer vacuum container, and means for minimizing the length of said head sections.
A related feature of the present invention utilizes a portion of the main body of the head section for crimping onto an end of said rod-like mid-section. The main body of the head sections themselves are threaded for connecting the assembled support rod from the supported structure to a base means on a support structure associated with the cryostat.